Non-volatile conductive inks

ABSTRACT

A method and composition for development of a latent electrostatic image with a liquid developer is disclosed. The non-volatile, non-hygroscopic, conductive liquid developer has a viscosity suitable for convenient application to an imaged surface in the development of latent electrostatic images. The developer composition comprises a coloring agent, a binder, and a dispersing agent in triethylene glycol monobutyl ether.

United States Patent Lu Sept. 23, 1975 [54] NON-VOLATILE CONDUCTIVE INKS 3.300.410 1/1967 Oliphant 252/621 3.535.244 10/1970 Zabiakm, .1 [75] Inventor: Chm H. Lu, Webster, NY. 354L682 11/1970 Mummy 4] 73 Assigneez Xerox Corporation Stamford 3,669,886 6/1972 Kosel .l

Conn.

. Primary E.raminer-Richard D. Lovering [22] Flled' May 1973 Attorney, Agent, or Firm.lames J. Ralabate; Donald [21] Appl. No.: 364,216 C. Kolaseh; Ernest'F. Chapman [52] US. Cl. 252/611; 8/93; 106/20; [57] ABSTRACT 106/311; gg gi gibfi A method and composition for development of a la- Int Cl 2 G03G'9/12 tent electrostatic image with a liquid developer is dis' closed. The non-volatile. non-hygroscopic, conductive [58] Fleld of Search 252/621 8/93 2 liquid developer has a viscosity suitable for convenient application to an imaged surface in the development of latent electrostatic images. The developer composi- [56] References cued tion comprises a coloring agent. a binder, and a dis- UNITED STATES PATENTS persing agent in triethylene glycol monobutyl ether. 3,084,043 4/1963 Gundlach 252/62.l X 3,290,251 12/1966 Nelson 252/62.l 9 Claims N0 Drawmgs N ON-VOLATILE CONDUCTIVE INKS BACKGROUND OF THE INVENTION This invention relates to electrostatic printing and more particularly to an improved ink and liquid developer composition for converting latent electrostatuc images into visible images.

In electrostatic printing, latent electrostatic images are formed on a photoconductive surface of a recording element by uniformly charging the surface thereof, as by a corona discharge device, followed by exposure to light in the desired image pattern. Such images may be developed by solid (powder) developers or by liquid developers.

Liquid developer compositions for use with electrostatic images generally comprise a dispersion of pig ment or toner particles in a volatile, insulating liquid of high volume resistivity in excess of ohm centimeters. Suitable insulating liquids include: aromatic hydrocarbons, such as benzene, toluene, and xylene; aliphatic hydrocarbons, such as, hexane, cyclohexane and heptane; freons and halogenated hydrocarbons and silicone oils. The liquid developer is applied to the imaged surface, and the suspended toner particles become electrostatically charged and develop the latent image by migration under influence of the image charge. This is known as electrophoretic development.

In another type of electrostatic image development disclosed by Gundlach in US. Pat. No. 3,084,043, liq uid developers having relatively low viscosity, low vola tility, contrast in color in the usual case with the surface on which it will remain, and relatively high electrical conductivity (relatively low volume resistivity), are disclosed for converting the electrostatic latent image to a visible image. According to this method liquid developer from a reservoir is deposited on a gravure roller and fills the depressions in the roller surface. Excess developer is removed from the lands between depressions, and as a receiving surface charged in image configuration passes against the gravure roller, developer is attracted from the depressions in image confiruration by the charge. This method of development is referred to as polar liquid development.

Print quality is difficult to control when prior art water and alcohol based inks are used as liquid developers. Evaporation can be a problem with the volatile prior art liquid developers, and when a volatile, conductive liquid carrier or solvent is organic in nature, evaporation results in pollution of the surrounding air, a very undesirable characteristic in view of the present day efforts to reduce or eliminate contaminants in the air.

The prior art liquid developers also are generally unsatisfactory from the standpoint of producing a permanent visible image which is free of smear or blurring especially when rubbed. This stems from the inability of the toner particles to become permanently fixed on the surface or in the fibers of the copy sheet. Other prior art liquid developers are somewhat hygroscopic and have a tendency to pick up moisture while standing and/or during application of the developer to the imaged surface thereby complicating the control of print quality and stability.

Certain non-epoxy ether-containing liquid develop ers in insulating carriers have been used in the development of electrostatic latent images. In US. Pat. No. 3,290,251 suitable ethers for use in insulating media include, for example, furane, dibutyl ether, diphenyl ether. ethylene glycol dimethyl ether, triethylene glycol dimethyl ether, ethylene glycol dibutyl ether, diethylene glycol diethyl ether and diethylene glycol dibutyl ether. However, these liquid developers are in a nonconductive, insulating medium, and therefore, they are not sufficiently conductive for use in the development of electrostatic latent images where the liquid developer is attracted to the image configuration without separation of the ingredients of the liquid developer. Furthermore, the developers disclosed therein are generally too volatile and tend to have varying compositions and properties due to evaporation. With these prior art compositions drying procedures must be used to permit evaporation of the solvent before the ink or developer becomes fixed to the substrate.

OBJECTS OF THE INVENTION Accordingly, it is a principal object of the present invention to provide a method and composition for development of a latent electrostatic image with a liquid developer free from the inherent dificiencies and disadvantages of prior art compositions and methods.

It is another object of this invention to provide a stable, conductive. non-volatile liquid developer composition wherein difficulty in control of print quality is essentially eliminated.

Still another object of this invention is to provide a liquid developer composition which is conductive, nonhygroscopic, and non-volatile. the ingredients of which remain in suspension upon standing, and which do not separate from the carrier medium when applied to the image surfaces during development of the latent electrostatic image.

Another object of this invention is to provide an ink or liquid developer composition which does not require heating or drying to fix the composition to the surface upon which it is applied.

Still further objects and advantages of the novel li uid developer .composition and method of the present invention will become apparent from the following more detailed description thereof.

SUMMARY OF THE INVENTION 1 have discovered that the above objects may be carried out by developing the electrostatic latent image with a liquid developer or ink composition comprising a binder, a coloring agent, a dispersing agent and triethylene glycol monobutyl ether .as the carrier or solvent. The invention lies in the discovery that when the ingredients are dispersed or dissolved in triethylene glycol monobutyl ether the resistivity is less than 10* ohmcentimeters; the viscosity is within the range at which liquid developers may be easily applied to surfaces and generally from about to 500 centipoises; the liquid is non-volatile and nonhygroscopic and does not separate upon standing; and the liquid migrates to the imaged surface without separation of the ingredients from the ether carrier to provide prints having excellent quality. The liquid developers of this invention when used in a copying process for the development of an electrostatic latent image, produce at a very low threshold voltage copies which exhibit unusually high contrast. l have found that the ink or liquid developer of my invention does not require any heating or drying to fix the composition to the surface to which it is applied.

l have also discovered a method for development of latent electrostatic images on asubstrate which comprises positioning close, but spaced from the electrostatic latent image on said substrate, a conductive, nonvolatile liquid developer having at least one binder, at least one coloring agent and at least one dispersing agent in the carrier or solvent, triethylene glycol monobutyl ether; providing flow aiding elements in physical contact between said developer and said substrate; and applying a bias to said developer whereby said developer moves along said flow aiding elements and thereby develops said electrostatic latent image and be comes fixed to said substrate with little or no evaporation in the absence of heat.

DESCRIPTION OF THE PREFERRED EMBODIMENTS it is critical in the practice of the present invention that the ingredients be dispersed or dissolved in the high boiling solvent, triethylene glycol monobutyl ether. The liquid developer composition comprises at least one binder, at least one coloring agent and at least one dispersing agent in the triethylene glycol monobu tyl ether.

The triethylene glycol monobutyl ether, otherwise known as butoxytriglycol, has a vapor pressure less than 0.0l mm Hg at 20 C. and a volume resistivity of approximately 1.6 X ohm-cm. The ink or liquid developer conductivity (resistivity) is mainly controlled by the triethylene glycol monobutyl ether, and the effects of binder, dispersing agent and coloring agent are generally relatively minor.

"To provide a liquid developer composition in accordance with the present invention it is preferred that the composition comprise at least about 40% by weight of the triethylene glycol monobutyl ether, however, it is important only that the composition comprise a balance of triethylene glycol monobutyl ether when the coloring agent is about l() weight percent, the dispersing agent is about 4-l0 weight percent and the binder is about l020 weight percent, and the optional additives, such as plasticizer, are present in quantities up to about 40 weight percent.

In the preferred embodiments of the present invention, pigment particles are suspended in the liquid carrier triethylene glycol monobutyl ether and are maintained in suspension by the aid of a dispersing agent dissolved therein. A binder is dissolved in the triethylene glycol monobutyl ether. In general, the compositions of the present invention comprise about 5% to of the coloring agent or pigment, about l7r to 10% of the dispersing agent, and about 5% to of the binder in the triethylene glycol monobutyl ether carrier liquid or solvent. Preferred ink or liquid developer compositions comprise about l02071 coloring agent. about 4l()7( dispersing agent, about 1020% binder and the balance triethylene glycol monobutyl ether. Percentages designated throughout the specification and claims are in weight percent. V

The suspended pigment or the dissolved dye or both are employed in that amount necessary to provide the desired positive print or copy when applied to a surface. There must be a sufficient anount of dispersing agent to maintain the dispersed pigment in suspension; and there must be an amount of binder sufficient to bind the coloring agent to the substrate. One skilled in the art can determine a suitable amount of binder, pigment and/or dye and dispersing agent for preparing a composition in accordance with the present invention. The concentrations of the various ingredients may be adjusted to prepare a formulation suitable as a liquid developer for use in the development of electrostatic latent images as long as the composition remains fluid and retains the other described properties. ln compositions of the type hereindescribed gelatin of the fluid occurs when certain additives are introduced into the composition and when certain of the ingredients are introduced into the composition at concentrations exceeding the limits in the above designated ranges. These gels have utility in certain printing operations, however, only those which retain a fluid consistency can be utilized as liquid for application to the imaged surface or its equivalent by gravure rolls or other applicators. One skilled in the art can adjust these parameters to provide compositions which remain fluid during the development process in the development of electrostatic latent images.

The amount of coloring agent, binder, and dispersing agent required to obtain the desired print or copy, the desired viscosity and the desired resistivity within the limits of the present invention depend to a certain extent upon the particular coloring agent, dispersing agent, and binder used in the triethylene glycol monobutyl ether. The most frequently useful ranges are described above. Suitable amounts of the particular ingredient for a particular ink or liquid developer can be readily determined by preparing several samples of the ink or liquid developer in question, adding different amounts of the particular ingredients to each of these samples and developing a standard electrostatic latent image with each of the so treated samples and comparing the print quality of each to determine the amount which provides the best results.

Suitable binders for use in the composition of the present invention include, for example, various resins and modified resins, such as, epoxy resins, phenolic resins, polyesters, and rosin esters. Certain preferred binders include modified phenolic resons, maleic rosin ester, modified rosin ester, glycerol ester of hydrogenated rosin, certain acrylic type resins, polyamide resins, and esterfied wood rosin. Any binder which will bind the pigment to the substrate and will not adversely interfere with the conductivity of the liquid developer, the quality of the print. the viscosity of the composition or cause the composition to gel upon standing, may be used in the practice of the present invention.

Pigments and dyes well known in the art may be used in the ink or liquid developer composition. Generally, such pigments as channel carbon black, furnace carbon black, and certain colored pigments are preferred in the practice of the present invention. In certain instances, dyes, for example, Hecto Blue R (C.l. Basic Violet 3, constitution no. 42555), which are soluble in the triethylene glycol monobutyl ether, may be used in place of the pigment or in conjunction with the pigment. However, the toner particles or pigments of the liquid developer composition can be selected from a wide variety of solid particles. Suitable organic or inorganic materials are described in the Carlson US. Pat. No. 2,297,691, including talcum powder, aluminumbronze, carbon dust and the like. The coloring agent may be in the form of pigment particles formulated of a suitable dyestuff or carbon black embodied in a resinous carrier, such as described in US. Pat. Nos.

2,907,674 and 2,891,91 1 The preferred amount of toner particles has been set forth above and is generally within about 520% by weight of the entire composi tion.

The dispersing agents for suspending or dispersing the pigment or coloring agent in the triethylene glycol monobutyl ether may be any of those agents which are generally utilized by one skilled in the art for dispersing such pigments in ink or liquid developer compositions. The amount of dispersing agent required to'maintin the pigment in suspension in the triethylene glycol monobutyl ether may also be adjusted by one skilled in the art. A preferred class of dispersing agent are the polyvinyl pyrrolidones or the alkylated polyvinyl pyrrolidones. Alkylated polymers of heterocyclic N-vinyl monomers may also be utilized as dispersents in preparing the composition of the present invention. Examples of these polymers and other alkylated polymers of com parable monomers are described in the U.S. Pat. No. 3,542,682.

The ink or liquid developer compositions of the present invention are non-volatile. Non-volatile are used herein means that the vapor pressure is below about 0.01 mm Hg (at C.).

The viscosity of the liquid developer or ink compositions of the present invention are between about 100 centipoises and 1,000 centipoises and are preferably below about 500 centipoises. The most preferred range for the viscosity of the ink or liquid developer of the present invention is about 250-50O centipoises at C.

If the viscosity of the ink or liquid developer is too high, the developer cannot be utilized in the devoloper of 1a tent electrostatic images in view of the fact that it will fail to migrate to the charged image configuration of the charged surface within the development time. On the other hand if the viscosity is too low, there will be too much liquid developer on the charged image area resulting in poor print quality.

The ink or liquid developer composition of the present invention must also be relatively nonhygroscopic when it is utilized in the development of latent electrostatic images, to prevent the absorption of moisture by the liquid developer with the resulting dilution of the developer by the moisture and a loss of viscosity within the range suitable for applying a liquid developer to the electrostatic latent image.

Other ingredients may be added to the ink or liquid developer composition of the present invention as long as such additives do not have a deleterious effect upon the conductivity, viscosity, or print quality. For example, certain plasticizers, such as dibutyl phthalate, diisodecyl adipate and triethylene glycol di(2- ethylbutyrate), may be added to the ink compositions.

Although the compositions of the present invention may be utilized in any type of liquid development of electrostatic latent images, one method for utilizing the composition of the present invention is disclosed by Gundlach in U.S. Pat. No. 3,084,043. In a method for the development of an electrostatic latent image on a substrate, the liquid developer composition of the present invention wherein the ingredients are dispersed or dissolved in triethylene glycol monobutyl ether, may be deposited upon a gravure type roller containing lands" and valleys and positioned close to, but spaced from, the electrostatic latent image on the substrate. in such a method it is preferred that the liquid developer be removed by a suitable means from the lands" of the gravure roll prior to the development of the electrostatic latent image on the substrate. Following this, a bias is applied to a developer so that the developer moves along the valleys of the gravure roll in the direction of the electrostatic latent image on the substrate in image configuration. Varoius modifications of this method may be made by one skilled in the art within the limits of the present invention which comprises applying in image configuration to the electrostatic latent image on a photoconductive layer, a non-volatile, non-hygroscopic liquid developer preferably having resistivity at 25C. of less than about 10 ohm-centimeters and a viscosity of about to 1,000

centipoises at 25 C. and comprising about 10-20 Weight percent of a coloring agent, about 4-10 weight percent of a dispersing agent, about 10-2O weight percent of a resin binder and the balance triethylene glycol monobutyl ether. Up to about 40. weight percent of the ink composition can also be a plasticizer.

Having described the basic ingredients of the composition of the present invention and the method by which the composition may be used, illustration will now be made of the formulation and use of various developing compositions representative of those of the present invention.

EXAMPLE 1 A composition was prepared having the following ingredients: 12% channel carbon black, 6% polyvinyl pyrrolidone dispersing agent, 15% modified phenolic resin, and 67% triethylene glycol monobutyl ether. The composition exhibited unusually high contrast development characteristics and required very low threshold voltage when utilized in the development of an electro staticlatent image. The resistivity of the ink was 3.0 X 10 ohm-cm, and the surface tension of the ink was 33.0 dynes/cm; it had an optical density of the hand proof of 1.19 and a Brookflield viscosity of 169 centipoises at 255 C.

EXAMPLE 11 A composition comprising 12.59? channel carbon black, 25% polyvinyl pyrrolidone dispersing agent, and 25% polyamide resin was dispersed or dissolved in 60% (by weight) ethylene glycol monobutyl ether. The com position had a resistivity of 6.7 X 10" ohm-cm., a viscosity of cp at 25C., and an optical density of 1.20, however, the composition was excessively volatile.

1n the examples viscosities were determined on a Brookfield viscometer and values are given in centipoises. Measurements were made at 12 RPM, 30 RPM. and 60 RPM, and the values given in the examples below were measured at 30 RPM unless otherwise indicated. A No. 2 spindle was used for the tests.

In most of the examples given below the optical density was determined in a sample of the ink was applied to a bond paper by a Pamarco Flexo Hand Proofer, allowed to dry, and measured with a Densichron Densitometer. The resistivity was measured in ohm-cm by using a manually balanced AC wheatstone bridge and a conductivity cell of 0.01 cell constant.

EXAMPLE 111 A composition containing 12% channel carbon black, 6% alkylated polyvinyl pyrrolidone dispersing agent having a molecular weight of 19,000 (weight average), and 15% modified phenolics resin (Beckacite EXAMPLE IV A composition having the same ingredients as disclosed for the composition of Example III was prepared with the exception that the dispersing agent was polyvinyl'pyrrolidone and the binder was the glycerol ester of hydrogenated rosin. The composition had an optical density of 1.15, a resistivity of 3.0 X 10 and a viscosity at C. of 163 centipoises. This ink or liquid developer composition in triethylene glycol monobutyl ether also produced excellent print density on paper and is suitable for use as a conductive liquid developer in copying processes.

EXAMPLE V A composition comprising 14% channel carbon black, 4alkylated polyvinyl pyrrolidone dispersing agent, 16% maleic rosin ester, 26% triethylene glycol monobutyl ether and 40% triethylene glycol di( 2-ethyl butyrate) plasticizer, was prepared. The composition had a resistivity of 1.9 X 10 ohm-cm. an optical density of 1.29 and a Brookfield viscosity of 376 centipoises at 25.3 C. The ink or liquid developer had excellent print density on paper, low volatility and a suitable viscosity for application by gravure-type rollers in the development of a latent electrostatic image. The composition did not take up and retain moisture on exposure to a humid atmosphere.

The above examples demonstrate the non-volatile, non-hygroscopic, conductive liquid developers or inks of the present invention which may be useful for the visual development of latent electrostatic images formed on a photoconductive layer.

While the present invention has been described primarily with respect to the foregoing specific examples. it is to be understood that the present invention is in no way to be deemed as limited thereto, but must be construed as broadly as all or any equivalent thereof.

I claim:

1. a non-volatile, non-hygroscopic, conductive ink consisting essentially of triethylene glycol monobutyl ether, about 5 percent to 25 percent coloring agent dispersible in said triethylene glycol monobutyl ether, about 1 percent to 10 percent of alkylated polymer of heterocyclic N-vinyl monomer dispersing agent for said coloring agent and about 5 percent to 30 percent binder soluble in said triethylene glycol monobutyl ether, said binder being selected from the group consisting of epoxy resins, phenolic resins, polyesters, rosin esters, acrylic type resins and polyamide resins.

2. The ink of claim 1 wherein the coloring agent is about 10 to 20 weight percent of the composition.

3. The ink of claim 1 wherein the dispersing agent is about 4 to 10 weight percent of the composition.

4. The ink of claim 1 wherein the binder is about 10 to 20 weight percent of the composition.

5. The ink of claim 1 wherein the triethylene glycol monobutyl ether is about 25 to weight percent of the composition.

6. The ink of claim 1 wherein the viscosity is less than about 1,000 centipoises at 25 C. and the resistivity is less that about 10 ohm-centimeters at 25 C.

7. The ink of claim 1 further including up to about 40 weight percent of a plasticizer.

8. A non-volatile, non-hygroscopic liquid developer for visual development of latent electrostatic images formed on a photoconductive layer, said liquid developer having a resistivity at 25C of less than l0 ohmcentimeters and a viscosity of about to 1.000 centipoises at 25C, comprising about 10-20 weight percent of a coloring agent capable of yielding color copies when attracted to a latent image, about 4 to 10 weight percent of a dispersing agent selected from the group consisting of polyvinyl pyrrolidones and alkylated polyvinyl pyrrolidones for said coloring agent, about 10 to 20 weight percent of a resin binder selected from the group consisting of epoxy resins, phenolic resins, acrylic type resins. polyamide resins, polyesters. and rosin esters, and the balance triethylene glycol monobutyl ether.

9. The liquid developer of claim 8 further comprising up to about 40 weight percent of a plasticizer.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT N0. 3, 0 ,6 4 Page 1 of 2 DATED v I September 23, I 1975 |NVENTOR(S) 2 i H, L

It is certified that error appears in the above-'-identified patent and that said Letters Patent is hereby corrected as shown-below:

Column 1, line 6, correctthe spelling of "electrostatic".

Column 1, line 22, capitalize the word "Freons".

Column 1, line 41, correct the spelling of the word 7 "configuration".

Column 2, line 22, correct the spelling of the word "deficiencies". V

Column 2, line 34, delete the word "surfaces" and substitute therefor --surface-.

Column 4, line 8, delete the phrase "hereindescribed" and substitute therefor described herein--.

Column 4, line 15, insert the word -developers-, following the word. "liquid".

Column 6, line 5, delete the word "latent" following the word "electrostatic".

Column 6, line 6, correct the spelling of "Various" Column 6, line 61, capitalize the word "Wheatstone" UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NC. 1 3, 07,594 Page 2 of 2 DATED September 23, 1975 mvemoMs); Chin H. Lu

It is certified that error appears in the above-identified patentand that said Letters Patent is hereby corrected as shown below:

Column 7, line 3, following the word "ohm cm" insert the word --and--.

Column 7, line 6, delete the word "has" and substitute therefor -had.

Column 7, line 25, following the numeral "4" kindly insert --percent' Signed and Scaled this .4 nest:

SIDNEY A. DIAMOND Arresting Ojficer Commissioner of Patents and Trademorks 

1. A ING ESSENTIALLY OF TRIETHYLENE GLYCOL MONOBUTYL ETHER, ABOUT 5 PERCENT TO 25 PERCENT COLORING AGENT DISPERSIBLE IN SAID TREITHYLENE GLYCOL MONOBUTYL ETHER, ABOUT 1 PERCENT TO 10 PERCENT OF ALKYLATED POLYMER OF HETEROCYLIC N-VINYL MONOR DISPERSING AGENT FOR SAID COLORING AGENT AND ABOUT 5 PERCENT TO 30 PERCENT BINDER SOLUBLE IN SAID TRIETHYLENE GLYCOL MONOBUTYL ETHER, SAID BINDER BEING SELECTED FROM THE GROUP CONSISTING OF EPOXY RESINS, PHENOLIC RESINS, POLYESTERS, ROSIN ESTERS, ACRYLIC TYPE RESINS AND POLYAMIDE RESINS.
 2. The ink of claim 1 wherein the coloring agent is about 10 to 20 weight percent of the composition.
 3. The ink of claim 1 wherein the dispersing agent is about 4 to 10 weight percent of the composition.
 4. The ink of claim 1 wherein the binder is about 10 to 20 weight percent of the composition.
 5. The ink of claim 1 wherein the triethylene glycol monobutyl ether is about 25 to 90 weight percent of the composition.
 6. The ink of claim 1 wherein the viscosity is less than about 1,000 centipoises at 25* C. and the resistivity is less that about 109 ohm-centimeters at 25* C.
 7. The ink of claim 1 further including up to about 40 weight percent of a plasticizer.
 8. A non-volatile, non-hygroscopic liquid developer for visual development of latent electrostatic images formed on a photoconductive layer, said liquid developer having a resistivity at 25*C of less than 109 ohm-centimeters and a viscosity of about 100 to 1,000 centipoises at 25*C, comprising about 10-20 weight percent of a coloring agent capable of yielding color copies when attracted to a latent image, about 4 to 10 weight percent of a dispersing agent selected from the group consisting of polyvinyl pyrrolidones and alkylated polyvinyl pyrrolidones for said coloring agent, about 10 to 20 weight percent of a resin binder selected from the group consisting of epoxy resins, phenolic resins, acrylic type resins, polyamide resins, polyesters, and rosin esters, and the balance triethylene glycol monobutyl ether.
 9. The liquid developer of claim 8 further comprising up to about 40 weight percent of a plasticizer. 